1. Field of the Invention
The present invention relates to a heat fixing member which applies heat and pressure to a recording material, and is disposed in a fixing apparatus which uses a heat and pressure fixing method, the fixing apparatus being used in an image formation apparatus using electro-photography such as a copier, a printer, facsimile machine and the like. The invention also relates to a heat and pressure fixing apparatus and an image formation apparatus which use said heat fixing member.
2. Description of the Related Art
Conventionally, in a copier, printer, etc. that utilizes an electro-photography, it is necessary to perform fixing of a unfixed toner image formed on a recording material, thereby making that unfixed toner image a permanent image. As a method for performing such fixing, there are known a solvent fixing method, a pressure fixing method, and a heat and pressure fixing method.
However, the solvent fixing method has the drawback that the solvent gives off vapor, and this causes problems in terms of odor and sanitation. On the other hand, the pressure fixing method has the drawback that the fixability is inferior to that obtained with the use of other mixing methods and that the pressure-sensitive toner is expensive. For those reasons, the solvent fixing method and pressure fixing method have not been put to practical use. The actual situation is that the heat and pressure fixing method has instead been generally widely used.
In the heat and pressure fixing method, the following technique is the most widely used. Namely, of a heating roll that is a heat fixing member and a pressure roll that is a pressure applying member, at least inside the heating roll, there is disposed a heat source. The both rolls are pressure-contacted with each other to thereby form a nip portion. And, while they are being rotated, a recording material having formed thereon a unfixed toner image is inserted through the nip portion. By doing so, the toner is molten and pressurized and is fixed onto the recording material. In this type of heating roll, on the surface of a hollow-cylindrical core metal, a heat-resisting release layer is provided as at least a surface layer. By doing so, the toner is prevented from adhering onto the heating roll. Particularly, if only color fixing apparatus are considered, there are many cases where, for the purpose of evenly conducting heat to the toner of each color, an elastic layer is provided between the core metal and the release layer. And this elastic layer may function to cover the laminated toners therein. On the other hand, the pressure roll is generally of a type wherein a heat-resisting elastic layer and, according to the necessity, a heat-resisting release layer are sequentially applied to the surface of the hollow-cylindrical or solid core metal.
In general, the thickness of the elastic layer is made greater than a certain value to thereby cause the deformation of the elastic layer of each of the rolls through the use of the nip pressure. The nip width is ensured by that deformation. Conventionally, the elastic layer is generally constructed of a heat-resisting rubber such as silicone rubber or fluorine rubber since these have large heat capacity. A time period of 3 to 8 minutes or so was needed for it to rise from room temperature. Thus in order to minimize the waiting period when a print job was received (or when there was an attempt to make a copy), even when the device was in a standby state, the temperature was kept at high temperature which was gather room temperature, but less than the temperature at which fixing is carried out. Because of this, most of the power consumed in the electro-photographic image formation apparatus was attributable to the operation of the fixing apparatus.
In order to solve this problem, decreasing the thickness of the heat fixing member as a whole is the most effective means. In order to obtain an excellent quality of fixed image,the thickness of the elastic layer must exceed a certain level. Especially, in a color copier/printer, toner images that correspond to 4 colors of yellow, magenta, cyan, and monochrome black are superposed one upon the other. Therefore, in order to equally conduct heat to the toner in a state in which all four color layers are superimposed and prevent the toner images from being mechanically brought out of their original shape, the the elastic layer must be used. An attempt has been made to realize reaching a temperature at which fixing is possible in a short period of time by making the hollow-cylindrical metal core which becomes the core metal thin.
However, if the core metal is simply made thin, the rigidity of the core metal decreases. For this reason, there occurs the inconvenience that the core metal flexes initially due to the nip pressure occurring between itself and the pressure member, or that the metal core undergoes permanent deformation of the core metal due to long use or being left unused. As a result, the nip pressure is unevenly applied in the circumferential direction of the heat fixing member. Thus, there defects of the fixed image quality such as gloss unevenness or fixation defects at the area where the nip pressure is low are caused.
In contrast, Japanese Patent Application Laid-Open Publications (JP-A) Nos. 59-155875 and 11-149226 each propose the following. Namely, on the inner surface of the core metal are rib is formed in parallel with the axial direction, or formed spirally, to thereby increase the mechanical strength of the heating roll. However, in this method, unevenness is substantially created in the thickness of the core metal. Consequently unevenness occurs in the direction of heat conduction from the heater (the heat source). Thus, there occurs a temperature difference between the rib-containing portion and the no-rib portion on the surface of the heating roll. This is considered to cause defects in the fixed image. In addition, ordinarily, the core metal can achieve a required precision by being made into a pipe by extrusion of metal such as aluminum or iron and thereafter being drawn off. However, in this case when a rib is formed in the inner surface of the core metal, it becomes necessary to perform a complex step in terms of the working. Consequently, the processing cost is also increased.
Also, JP-A No. 10-240059 has proposed a method of increasing the mechanical strength by making a composite from an aluminum core metal and a resin layer. In this method, though, it is certainly possible to decrease the thickness of the aluminum core metal, because a resin such as epoxy constituting the resin layer is inferior in the conduction of heat to metal, there occurs the drawback that the period needed to reach to a temperature at which fixing is possible becomes large. Also, the adherence at the interface between the aluminum and the resin layer, or the durability thereof, is not sufficient. Therefore, when consideration is given to the fact that the core metal when used as a fixing member is used in an environment of high temperature, and that peeling occurs at the interface due to use for a long period, the core metal does not have sufficient mechanical strength.
Further, JP-A No. 2-149628 has proposed an invention that concerns an aluminum alloy having 1.0 to 5.0% Mn as an additive that is added to the aluminum itself. However, it cannot be said that that alloy having that composition ratio exhibits a sufficiently high level of extrusion workability. This leads to an increase in the working cost. Furthermore, bends that occurs due to use for a long period at a high temperature are likely to be formed.
Accordingly, the present invention has been made in order to solve the problems inherent in the above-described conventional techniques and has an object to provide a heat fixing member which while maintaining an image that is has a high image quality, enables shortening of the length of time needed until a temperature at which fixing is possible is reached, and a heat and pressure fixing apparatus that uses the heat fixing member. Another object of the present invention is to provide a highly durable heat fixing member which even when used for a long period of time and at a high temperature is prevented from being bent, and a heat and pressure fixing apparatus that uses the heat fixing member. A third object of the present invention is to provide an image formation apparatus that uses the heat and pressure fixing apparatus having such excellent characteristics.
The inventors of this patent application have discovered that the above-described problems can be solved by defining the characteristics of the materials that are used as the core metal of the heat fixing member, and this has led to the present invention. Namely, the present invention is as follows. A first aspect of the present invention is a heat fixing member for applying heat and pressure to the recording material in a fixing apparatus in order to fix an unfixed toner image carried thereon, the heat fixing member comprises:
a cylindrical core metal; and
a release layer formed on a peripheral surface of the core metal, wherein the thickness of the core metal is 2.8 mm or less, and the core metal is formed of a material which is elastically deformed by a stress of 60.0 MPa in an environment of 210xc2x0 C.
The heat fixing member according to the first aspect of the present invention, wherein the thickness of the core metal is no less than 0.5 mm.
The heat fixing member according to the first aspect of the present invention, wherein the core metal is formed of an aluminum alloy.
The heat fixing member according to the first aspect of the present invention, wherein the outer diameter of the core metal is from 20 to 40 mm. The heat fixing member according to the first aspect of the present invention, wherein the release layer consists of a fluorine containing polymer material.
The heat fixing member according to the first aspect of the present invention, wherein the thickness of the release layer is from 10 to 100 xcexcm.
The heat fixing member according to the first aspect of the present invention, wherein at least an elastic layer is formed between the core metal and the release layer. The elastic layer may consist of silicone rubber, and the thickness of the elastic layer may be from 50 xcexcm to 1.0 mm.
A second aspect of the present invention is a heat and pressure fixing apparatus for applying heat and pressure to a recording material in order to fix an unfixed toner image carried thereon, the heat and pressure fixing apparatus comprises:
a cylindrical heat fixing member;
a pressure applying member which is press-contacted with a peripheral surface of the heat fixing member to form a nip portion therebetween, through which the recording material is inserted; and
a heat source disposed inside the heat fixing member, wherein the heat fixing member includes a core metal and a release layer formed on a peripheral surface of the core metal, the thickness of the core metal is from 0.5 mm to 2.8 mm, and the core metal is formed of an aluminum alloy that is elastically deformed by a stress of 60.0 MPa in an environment of 210xc2x0 C.
The heat and pressure fixing apparatus according to the second aspect of the present invention, wherein the diameter of the core metal is from 20 to 40 mm.
The heat and pressure fixing apparatus according to the second aspect of the present invention, wherein the release layer consists of a fluorine containing polymer material.
The heat and pressure fixing apparatus according to the second aspect of the present invention, wherein the thickness of the release layer is from 10 to 100 xcexcm.
The heat and pressure fixing apparatus according to the second aspect of the present invention, wherein at least an elastic layer is formed between the core metal and the release layer.
The heat and pressure fixing apparatus according to the second aspect of the present invention, wherein the elastic layer consists of silicone rubber.
The heat and pressure fixing apparatus according to the second aspect of the present invention, wherein the thickness of the elastic layer is from 50 xcexcm to 1.0 mm.
The heat and pressure fixing apparatus according to the second aspect of the present invention, wherein heat and pressure is applied to the recording material by the heat fixing member being heated at a temperature of 100 to 210xc2x0 C. and a load being applied thereto by the pressure applying member so as to provide a stress of no more than 60.0 MPa.
The heat and pressure fixing apparatus according to the second aspect of the present invention, wherein the pressure applying member includes an endless belt and a presser disposed inside the endless belt, the endless belt being wound around the heat fixing member at a predetermined angle to form a nip portion between the endless belt and the heat fixing member, through which a recording material is inserted, and a strain is caused on the surface of the heat fixing member by pressing the presser against the heat fixing member via the endless belt at the nip portion. The presser may be a pressure pad, and a nip pressure of the pressure pad that presses the heat fixing member may be locally large in the vicinity of an exit of the nip portion.
A third aspect of the present invention is a heat and pressure fixing apparatus for applying heat and pressure to a recording material in order to fix the unfixed toner image which is carried toner image thereon, the fixing apparatus comprises:
a cylindrical heat fixing member;
a pressure applying member that is press-contacted with a peripheral surface of the heat fixing member to form a nip portion through which the recording material is inserted; and
a heat source disposed inside the heat fixing member, wherein the heat fixing member includes a core metal and a release layer formed around the core metal, the thickness of the core metal is no more than 2.8 mm, and at the time of fixation the heat fixing member is elastically deformed by a load applied so as to produce a stress of no more than 60.0 MPa from the pressure applying member.
The heat and pressure fixing apparatus according to the third aspect of the present invention, wherein the load applied to the heat fixing member by the pressure applying member produces a stress of no less than 25.0 MPa.
A fourth aspect of the present invention is an image formation apparatus, comprises:
an electrostatic latent image formation device that forms an electrostatic latent image on an electrostatic latent image carrier;
a development device which develops the electrostatic image by the use of toner;
a transfer device which transfers the developed toner image onto a recording material; and
a fixation device which fixes the transferred toner image on the recording material, wherein the fixation device includes a cylindrical heat fixing member, a pressure applying member which is press-contacted with a peripheral surface of the heat fixing member to form a nip portion through which the recording material is inserted, and a heat source that is disposed inside the heating fixing member, and the heat fixing member includes a core metal and a release layer formed on the peripheral surface of the core metal, and wherein the thickness of the core metal is from 0.5 mm to 2.8 mm, and the core metal is formed of an aluminum alloy that is elastically deformed by a stress of 60.0 MPa in an environment of 210xc2x0 C.
A fifth aspect of the present invention is an image formation apparatus comprises:
an electrostatic latent image formation device forming an electrostatic latent image on an electrostatic latent image carrier;
a development device which develops the electrostatic image by the use of toner;
a transfer device which transfers the developed toner image onto a recording material; and
a fixation device which fixes the transferred toner image on the recording material, wherein the fixation device includes a cylindrical heat fixing member, a pressure applying member which is press-contacted with a peripheral surface of the heat fixing member to form a nip portion through which the recording material is inserted, and a heat source that is disposed inside the heat fixing member, and the heat fixing member includes a core metal and a release layer formed on the peripheral surface of the core metal, the thickness of the core metal is no more than 2.8 mm, and at the time of fixation the heat fixing member is elastically deformed by a load applied so as to produce a stress from the pressure applying member of no more than 60.0 MPa.
One feature of the present invention is using as a material for the core metal of the heat fixing member, a material that can be elastically deformed even under conditions where the maximum stress of the fixing load is applied and the temperature is the upper limit of the temperature range for fixing.
In general, up until now, a material for a core metal of the heat fixing member which can be left unused for a long period, and which has the pressure applying member and the nip portion formed, has been suitably selected based on JIS standards (in the case of an aluminum alloy, JIS-H0001 etc.). The selection is made such that the strength is sufficient for the purpose for which it is to be used. However, since some materials which are suitable based on the characteristic values prescribed by some of the JIS standards do not exist, errors were sometimes made in the important selection of the material. Generally, such physical-characteristic values of the material are the ones that have in many cases are measured at normal temperature. Also, the physical characteristic values include, such values as the proof stress, mechanical strength, or creep deformation as measured with the tensile test. Accordingly, when the state of use inside the fixing apparatus is given sufficient consideration, it is virtually impossible to simply select the relevant suitable material based on the characteristic values described in JIS standard.
On that account, the inventors of this patent application first have considered the circumstances under which a material is used as the heat fixing member. And in order to find a high-strength material with that taken into consideration, they have come up with the following. Namely, a core metal is fixed in a state of being supported at each of its ends and in a state of high temperature state which is at the upper-limit of temperature at which fixing is possible range for fixing. They then have then, when the core metal has been fixed as such, a load may be applied, as one-point load, to the center of the core metal so that, when a fixation load has been applied, the resulting stress is the greatest or maximum. And they have selected a material for the core metal which is not substantially deformed before or after the time when that load is applied. (Namely, a material that is elastically deformed, even under the conditions where it the maximum stress is generated, by the fixation load, at the upper-limit temperature of the temperature at which fixing is possible range for fixing.) They thereby have discovered that such selected material can exhibit a strength that corresponds to the circumstances of use thereof as the heat fixing member. Further, by defining the thickness of that material, they have also discovered that it is possible to obtain the heat fixing member in which period of time needed until a temperature at which fixing is possible is reached, is decreased (i.e. which has excellent instant startability characteristic).
Further, through using the above-described heat fixing member and again through defining the temperature and load (stress) of the heat fixing member during the use thereof, they have also discovered the following. That is, they have discovered a heat fixing apparatus (hereinafter there are cases in which it is referred to simply as xe2x80x9cthe fixing apparatusxe2x80x9d) that has excellent startability characteristic and that exhibits no deformation of the heat fixing member even when it is left to stand for a long period of time.
That is, through applying to the fixing apparatus the heat fixing member based on the use of the material satisfying the characteristic defined in the present invention, it is possible, while maintaining the quality of the obtained image at a high level, to shorten the length of time needed until a temperature at which fixing is possible is reached.